Implement a consistent hashing ring

Implement a class `ConsistentHashRing` that distributes keys across servers using a hash ring with virtual nodes. Required API: - `ConsistentHashRing(replicas_per_server: int)` - `add_server(server_id: str) -> None` - `remove_server(server_id: str) -> None` - `get_server(key: str) -> Optional[str]` Behavior: - Use any deterministic hash function that maps a string to a 32-bit integer. - When a server is added, create `replicas_per_server` virtual nodes at positions `hash(server_id + "#" + i)` for `i = 0..replicas_per_server-1`. - `get_server(key)` computes `hash(key)` and returns the server owning the first virtual node found when moving clockwise around the ring. - If there is no virtual node with position greater than or equal to `hash(key)`, wrap around and return the server at the smallest position. - If the ring is empty, return `None`. - Removing a server removes all of its virtual nodes. Target complexity: - `add_server` / `remove_server`: `O(R log N)` where `R` is the number of replicas added or removed - `get_server`: `O(log N)`